The present invention relates to semiconductor elements, more particularly, to those for use in communication, information processing and the like which are adapted to convert incident or input light having a given wavelength to outgoing or output light having a desired wavelength.
In the field of light information processing, light switching and the like in which processing of information is carried out using light which carries or bears information without converting light signals to electric signals, it has been desired to realize a wavelength conversion element which can convert input light having a given wavelength to output light having a desired wavelength since such element allows processing of information in large capacity by means of multiplex wavelengths.
Conventional types of wavelength conversion elements heretofore proposed include one which utilizes generation of second harmonic wave that is non-linear optical effect and which achieves wavelength conversion to half the original wavelength. More particularly, as Taniuchi et al. reported in an international conference, i.e., Conference on Lasers and Electro-optics, 1986, introduction of a semiconductor laser beam having a wavelength of 0.84 .mu.m in an amount of 40 mW into a proton-exchanged light waveguide of lithium niobate substrate generates a laser beam having a wavelength of 0.42 .mu.m in an amount of 0.4 mW (WR3 presentation). However, the conventional wavelength conversion element utilizing generation of second harmonic wave is disadvantageous since it only allows conversion of wavelength to half the wavelength of the input light.
On the other hand, in semiconductor lasers whose lasing wavelength can be tuned electrically, various types of semiconductor lasers are known as described, for example, in Y. Abe et al., Electronics Letters, vol. 17, No. 25, 10th December 1981, pages 945-947 which discloses integrated lasers with butt-jointed built-in distributed Bragg reflection waveguides in which an active guide and a built-in external guide on the surface of which is formed corrugation are butt-jointed.
Furthermore, there have been proposed multi-electrode distributed feedback reflector type semiconductor lasers as described in, for example, JP-A-No. 61-290789 which discloses a multi-electrode distributed feedback type semiconductor laser device comprising a diffractive grating over the whole length of the resonator and at least two electrodes in the direction of light axis, the electrodes being controllable with respect to their injection current supply independently of each other.